1. Field of the Invention
This invention relates to blood collection and, more particularly, relates to a plastic blood sample collection assembly.
2. Background
Blood samples are routinely taken in glass evacuated tubes. One end of a double-ended needle is inserted into a patient's vein. The other end of the needle then punctures a stopper covering the open end of the tube so that the vacuum in the tube draws the blood sample through the needle into the tube. Using this technique, a plurality of samples can be taken using a single needle puncture of the skin.
Plastic tubes have also been proposed for blood collection. Plastic offers a number of advantages over glass such as lower breakage, less weight in shipment, and easier disposal by incineration.
Blood collected in evacuated tubes often must be clotted prior to clinical examination. It is desirable to form a dense clot as rapidly and completely a possible to facilitate clean separation of the clot from the serum layer by centrifugation. To achieve this end, both plastic and glass blood collection tubes frequently employ a clot activator.
Practically all commercial blood collection tubes include particulate activators which lead to dense, crosslinked clots that cleanly separate from the serum in a hematological centrifuge. Clot formation, however, is relatively slow, particularly in plastic, and about 30-60 minutes are required prior to centrifugation. Typical particulate activators used commercially are silica impregnated in fabric, silica particles in small plastic cups or silicate particles applied to the tube wall in polyvinylpyrrolidone (PVP). When blood enters a tube containing silicate-PVP, the PVP dissolves and the silicate particles are released. The PVP enters both the serum and the clot and may interfere with chemical or hematological assays and may foul automated and/or optical instruments.
There is a need in the art for a clot activator which rapidly forms a dense clot which separates cleanly from the serum on centrifugation without contaminating the serum with soluble chemicals. The present invention is directed to fulfilling this need.